U.S. Pat. No. 5,040,589 (Filed: Feb. 10, 1989; Inventor: Bradley et al; Assignee: The Dow Chemical Company, U.S.A.) discloses forming a plug of solid metal (in a nozzle of an injection molding machine) from a residue of molten metal that remains after a mold cavity is filled. A conduit passageway has a volume of molten metal located upstream of a formed metal plug (that is, a blockage). This arrangement appears to have become an established approach for configuring molten metal conduit passageways, and this approach has not changed since the filing date of this patent (as will be demonstrated in a review of the state of the art below). The formed (solid) plug is injected into a mold, and the plug is caught in a plug catcher so that the plug is thus prevented from entering the mold cavity defined by the mold. The plug becomes a vestige that needs to be removed from the molded article (in which case, the removed plug represents a waste of molding material). For molded articles having a large size, this arrangement may or may not represent a problem. However, for smaller molded articles (such as cell-phone housings, laptop housings, etc), this arrangement may represent a problem.
Published article titled Semi-solid Forming of Aluminum and Magnesium (Publication date: June 1996; Author: A. I. “Ed” Nussbaum; Journal Name: Light Metal ABE) discloses a mold cavity which has a catcher that catches a metallic plug so that the plug, once caught, does not impede the flow of molten metal into the mold cavity.
PCT Patent Application No. WO/9928065A1 (Filed: Nov. 30, 1998; Inventor: Murray et al; Assignee: Commonwealth Scientific and Industrial Research Organisation, Australia) discloses a metal molding system that includes a conduit passageway having a volume of molten metal located upstream of a plug (that is, a blockage). This arrangement appears to conform to the industry-accepted approach for injecting molten metal into a mold cavity.
U.S. Pat. No. 6,533,021 (Filed: Sep. 14, 2000; Inventor: Shibata et al; Assignee: Ju-Oh Inc., Japan, and The Japan Steel Works Ltd., Japan) discloses a metal molding system that includes a conduit passageway having a volume of molten metal located upstream of a plug (that is, a blockage). The plug is blocked from entering a mold cavity and then it becomes partially melted (by a heater) so that molten metal may flow past the plug. Since the plug is blocked from entering the mold cavity, the plug partially resists the flow of molten metal. This arrangement may reduce the quality of the molded part and/or may increase cycle time needed to mold an article. If the plug is melted before injection pressure is applied, the molten metal begins to drool (and a potentially low-quality part may be formed). If the plug is melted after the injection pressure is applied, the plug may become jammed in an entrance leading into a mold cavity and then the plug acts to restrict (at least in part) flow of the molten metal flowing from upstream toward downstream and then into the mold cavity (and potentially increase cycle time). The timing of when to begin heating the plug (relative to when injection pressure is actuated) may be difficult to achieve on a repeatable and reliable basis.
U.S. Pat. No. 6,938,669 (Filed: Aug. 28, 2002; Inventor: Suzuki et al; Assignee: DENSO Corporation, Japan) discloses a metal molding system that includes a conduit passageway having a volume of molten metal located upstream of a plug (that is, a blockage). This arrangement appears to conform to the industry-accepted approach for injecting molten metal into a mold cavity.
PCT Patent Application No. WO/03106075A1 (Filed: May 5, 2003; Inventor: Czerwinski et al; Assignee: Husky Injection Molding Systems Limited, Canada) discloses a metal molding system that includes a conduit passageway having a volume of molten metal located upstream of a plug (that is, a blockage). This arrangement appears to conform to the industry-accepted approach for injecting molten metal into a mold cavity.
U.S. Patent Application No. 2005/0006046A1 (Filed: Aug. 10, 2004; Inventor: Tanaka et al; Assignee: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd), Japan) discloses a metal molding system that includes a conduit passageway having a volume of molten metal located upstream of a plug (that is, a blockage). An injection pressure injects the plug, which is followed by a flow of the volume of molten metal into the mold cavity. The mold cavity has a catcher that catches the injected plug so that it remains offset from the molten metal that flows into the mold cavity (thereby the plug does not resist or impede the flow). This arrangement appears to be an industry-accepted approach that results in a molded article having a (potentially large) vestige that includes the plug embedded therein. A large vestige may cause heat deformation of the molded part if the vestige is formed on a thin wall (of the molded part) because the vestige has a thermal mass which may cool slower than the mass of the thin wall. This arrangement may result in increased manufacturing costs since the large vestige represents a waste of material and/or requires effort to remove it from the molded article, and/or represents a limit as to how thin the molded article can be made.
It appears that the metal molding process as described above (established over a 15 year period without apparent deviation) is to pass, through a passageway conduit, a volume of molten metal that is located upstream of a passageway blockage (that is, upstream in a sense that the shot is located between the plug and an injection unit of the metal molding system), and that the way to manage the plug is to catch it in a plug catcher.